The T3 uptake blood test is a laboratory test that measures the level of thyroxine-binding globulin (TBG) in the blood. TBG is a protein that binds to thyroid hormones, including triiodothyronine (T3) and thyroxine (T4), and helps to transport them through the bloodstream to the body’s tissues.

The T3 uptake test is not a direct measure of T3 levels, but rather an indirect measure of the amount of TBG that is available to bind to T3. A low T3 uptake indicates that more TBG is bound to T3, while a high T3 uptake indicates that less TBG is bound to T3.

The T3 uptake test is commonly used as part of a panel of tests to evaluate thyroid function and to diagnose and monitor thyroid disorders, such as hypothyroidism and hyperthyroidism. It can also be used to evaluate other conditions, such as liver disease and malnutrition.

During the test, a small sample of blood is drawn from a vein in the arm and sent to a laboratory for analysis. The normal range for T3 uptake levels varies depending on the laboratory that performs the test, but generally ranges from 22% to 35%.

Abnormal T3 uptake levels can indicate thyroid dysfunction or other conditions. A low T3 uptake, indicating more TBG bound to T3, may be seen in conditions such as hypothyroidism, liver disease, and pregnancy. A high T3 uptake, indicating less TBG bound to T3, may be seen in conditions such as hyperthyroidism and malnutrition.

A healthcare provider can interpret the results of the T3 uptake blood test in the context of the individual’s medical history and other test results, and develop an appropriate treatment plan if necessary.